I would say to get out of the habit of including it, unless you really need it. Not all errors are static. It could depend on the variable content, or if Windows had it's finger up it's butt when you tested it. Could also be the response from the smtp server being used.

Whatever it was, if it ain't broke, don't fix it. I've never used the exclamation point in any of my sendmail code, and it's always worked.

Wrangler--------------"You never know about a woman. Whether she'll laugh, cry or go for a gun." - Louis L'Amour

Yes, you're right. Looking for this I found a plenty of information, this it isn't exclusive of Neobook. But I saw 5.7.0 and I though it was some of this version because in the 5.6.4a, till this moment, it never appeared to me.

*UPDATE*

I notice that Yahoo smtp server works, but Hotmail or Gmail don't. Then, same problem in 5.7b or 5.6.4a with these servers.